Penicillin content of blood serum after various doses of penicillin by various routes.

In this paper Fleming and colleagues explained how to choose routes of administration of penicillin as well as dosage, and reproduced the graphs/figures that showed blood levels achieved with different doses and routes of administration.
Fleming was the first to use Procaine mixed with penicillin in order to alleviate the tremendous intramuscular pain of the injections. He showed that the anesthetic did not affect the bacterial killing power of the antibiotic. With M. Y. Young, A. J. E. Rowe.

(Thanks to Juan Weiss for this reference and its interpretation.)